The fundamental problem with your hypothesis is the time-value of money: overnight deposits can be moved around, well, overnight, but a 30yr bond (for the bondh

The fundamental problem with your hypothesis is the time-value of money: overnight deposits can be moved around, well, overnight, but a 30yr bond (for the bondholder, ignoring secondary markets) locks up capital for decades. A bondholder can't take advantage of future preferential interest rates when their capital is already locked up in low-yielding bonds. This is why bond price and bond yields have an inverse relationship.